This project utilizes the strengths and talents of a multi- disciplinary and inter-institutional group of investigators to study the natural history of HIV infection in a heterosexual population of South Central Los Angeles County. The design is a parallel one to that of the MACS study in which UCLA is a collaborative institution. The first objective is to estimate the prevalence of HIV infection in the general public and in those attending the STD clinics of four health districts in South Central Los Angeles County. To accomplish this, radio, television and news media advertisement will be made to inform the public of the availability of free, confidential testing. Also, on-site community workers will be referring STD clinic attendees of the King/Drew Medical Center for testing. The second objective is to study the natural history of HIV infection in a group of HIV(+) individuals, a comparison group of HIV(-) individuals, and a group of HIV(-) individuals who are the heterosexual partners of AIDS or ARC victims. These people will be followed prospectively with semi-annual examinations and testing. The data obtained from this aspect of the project will provide useful clues to the factors and cofactors related to the progression of HIV(+) status to AIDS or ARC.